Anest. intenziv. Med. 2025;36(3):198-202 | DOI: 10.36290/aim.2025.034

The physiology of acid-base balanceClinical physiology

Duška F.

Klinika anesteziologie a resuscitace 3. lékařské fakulty Univerzity Karlovy a Fakultní nemocnice Královské Vinohrady, Praha

Acid-base balance is a key component of internal homeostasis, essential for enzyme function, cellular signaling, and ATP synthesis. The physiological mechanisms that maintain a stable pH in the extracellular fluid include acid production, buffering, and elimination. The body continuously generates both volatile acids (CO₂) and non-volatile acids (e.g., lactate, sulfate, phosphate). CO₂ is excreted by the lungs, while non-volatile acids are partly metabolized and partly excreted by the kidneys. Blood buffering systems-particularly the bicarbonate buffer, hemoglobin, and plasma proteins-help mitigate acute changes in pH. To assess acid-base balance, both the classical Henderson-Hasselbalch approach, based on the [HCO₃^-]/pCO₂ ratio, and the physicochemical Stewart model are used. The Stewart model highlights the role of strong ion difference (SID), concentrations of weak acids, and pCO₂ as independent determinants of acid-base status. Respiratory regulation through changes in ventilation directly affects pCO₂, while renal regulation modifies urine composition and enables long-term correction of pH through ammoniagenesis and bicarbonate reabsorption. Inter-organ substrate fluxes, such as glutamine transport between the liver and kidneys, also plays a significant role. Infused fluids affect acid-base balance depending on the quantity of metabolisable organic anions. Understanding these principles is essential for making clinical decisions regarding ventilation settings, fluid therapy, and correction of electrolyte disturbances. The goal of treatment should not be the mechanical normalization of laboratory values, but rather the support of physiological compensatory mechanisms in the context of the underlying disease.

Keywords: acid-base balance, hydrogen ion concentration, buffers, kidney physiology, respiratory physiology.

Received: June 11, 2025; Revised: June 11, 2025; Accepted: July 22, 2025; Prepublished online: September 26, 2025; Published: September 30, 2025  Show citation